The evaluated Field can be set to be required, which means that if the Field that gets shown can receive input, it must be filled in (e.g. if a text Field is shown, it is required, but if a link Field is shown, nothing is required). ​ This same sort of tranference applies to the view-only setting in the Values and Auditing tab of the Block Editor: if the resulting Field normally would be in add/edit mode, checking view-only forces it to be in view mode.